CALCULATION OF RESULTS. 73 



COMPRESSION OF AIR IN ABSORBING SYSTEM. 



A second fluctuation in volume is due to the fact that, as air is forced 

 through the absorbing system, the increased pressure required causes 

 portions of the air to be somewhat compressed. The chief resistance 

 to the passage of the air is furnished by the layer of sulphuric acid in 

 the two water-absorbers. When the acid in the absorbers is fresh, 

 i. c., when 3.5 kilos of acid of the specific gravity of 1.84 is in each, 

 the pressure is not far from 35 mm. of mercury. The resistance of the 

 soda lime in the carbon-dioxide absorbers to the passage of the air has 

 been found by actual experiment to be relatively insignificant. 



The actual measurement of air in the system is made, however, at 

 the period of changing from one absorbing system to the other, i. e., 

 at the end of each experimental period. Under these conditions, there- 

 fore, since the air in all other parts of the circulating system is at 

 atmospheric pressure, we have to do only with the air in the first water- 

 absorber and the three carbon-dioxide absorbers. When the blower is 

 stopped the compressed air leaks back through the blower into the 

 system, and the pressure on that portion of the air confined between 

 the blower and the level of the sulphuric acid in the entrance pipe of 

 the first water- absorber becomes atmospheric. Since the exhaust tube 

 from the last water- absorber connects directly through the main air-pipe 

 to the chamber, the air above the acid in this absorber is likewise at 

 atmospheric pressure. The air above the sulphuric acid in the first 

 water-absorber, as well as the air in the three carbon-dioxide absorbers 

 and that small portion confined in the entrance pipe of the last water- 

 absorber, remains, however, under a somewhat increased pressure. 

 Consequently, in order to obtain the true volume of air in that portion 

 of the absorbing system under increased pressure, it was formerly nec- 

 essary to correct the volume for the increased pressure. By a simple 

 process of calculation it was found that the difference in the volume of 

 the air confined in this portion of the absorber system at atmospheric 

 pressure and under the slightly increased pressure amounted to not far 

 from 0.4 liter. There was therefore a discharge of air from the system 

 as a whole amounting to 0.4 liter every time the absorbing system was 

 changed. 



As a verification of the calculations, provision was made to allow 

 the compressed air to escape through the Elster meter, the amount es- 

 caping being thus measured accurately. This was found to be almost 

 invariably 0.4 liter. 



In the more recent experiments, when the plan for testing the ab- 

 sorbing system described on page 32 was put in operation, this correc- 

 tion for the air contained in the absorbers at the end of this period has 



